First, make the fractions unsimplified
10/3 and 12/5
Then, you need common denominators. Because it is the least common multiple, make the denominators 15 by multiplying the numerator and denominator of 10/3 by 5. Make the denominator 15 by multiplying the numerator and denominator of 12/5 by 3.
Your new fractions will be 50/15 and 36/15
Subtract
50/15-36/15=14/15.